No one wants a hacking cough for days or weeks on end. But research shows that it generally takes about 18 days to get over a standard cough-based illness. Most of us grow impatient after a week or so and head to the doctor to get a prescription. The problem with that recourse, however, is that antibiotics are usually useless against typical respiratory infections that cause coughs.

A new analysis shows that even though antibiotics might be ineffective against a lingering cough, the timing of their prescription might be fooling people into thinking that the medication worked. This pattern might increase the frequency of these unnecessary prescriptions, a hazardous practice that can increase drug resistance across many bacteria strains. The findings were published online January 14 in Annals of Family Medicine.

A cough is one of the most common reasons patients go to the doctor. One quick fix, patients might assume, is a round of antibiotics. Not exactly, according to a randomized trial described last month in The Lancet Infectious Diseases. The trial showed little difference in the duration of lower-respiratory infections in people who got antibiotics and those who received placebos. Why? Like the full-blown flu, coughs are usually triggered by viruses—not bacteria—and thus are unaffected by antibiotics. Most often coughs and associated infections get better on their own. This happy outcome, however, can cause some confusion about the efficacy of antibiotics for treating cough-based sicknesses.

The researchers for the new study, led by Mark Ebell of the Department of Epidemiology and Biostatistics in the College of Public Health at the University of Georgia, combed through data on acute coughs. They found that the average duration of symptoms reported in the medical literature was 17.8 days. They then compared these findings to results from a poll of 500 adults, who were asked to estimate how long they would expect to be sick if their main symptom was a cough and they were not taking any medicine (under various scenarios with or without fever and with or without mucus). The expected duration was about seven to nine days (on the longer side if the cough was accompanied by a fever or green mucus). In other words, far less than the mean duration of these types of ailments.

"This mismatch between patients' expectations and reality for the natural history of acute cough illness has important implications for antibiotic prescribing," the authors noted in their paper. As they explained, if a patient has not started getting better after about a week—when they expect the cough should be tapering off—they might head to the doctor to get antibiotics. This timing, however, is troublesome. "If they begin taking an antibiotic seven days after the onset of symptoms, they may begin to feel better three or four days later, with the episode fully resolving 10 days later," the researchers wrote. "Although this outcome may reinforce the mistaken idea that the antibiotic worked, it is merely a reflection of the natural history" of the illness.

Helping patients understand this common coincidence—and the actual expected duration for their cough—could help reduce the amount of antibiotics needlessly prescribed for such ailments. Unnecessary antibiotic prescriptions can contribute to the growing trend of antibiotic resistance, which reduces the efficacy of these drugs in situations in which they really are needed.

Doctors often give in to pressure from patients to prescribe "something" for their illness. "Patients should be told that it is normal to still be coughing two or even three weeks after onset, and that they should only seek care if they are worsening or if an alarm symptom, such as high fever, bloody or rusty sputum, or shortness of breath, occurs," Ebell and his colleagues wrote. Otherwise, a thoughtless "quick-fix" Rx is likely to just "increase the belief in their efficacy, creating the potential for a cycle of expectation and prescription," the researchers noted. And that is not good for anyone's health.